Automatic dishwashing detergents constitute a generally recognized distinct class of detergent compositions whose purpose can include to breakdown and remove food soils; to inhibit foaming; to promote the wetting of wash articles in order to minimize or eliminate visually observable spotting and filming; to remove stains such as might be caused by beverages such as coffee and tea or by vegetable soils such as carotenoid soils; to prevent a buildup of soil films on wash ware surfaces; and to reduce or eliminate tarnishing of flatware without substantially etching or corroding or otherwise damaging the surface of glasses or dishes.
The problem of glassware corroding during washing the cycle of an automatic dishwashing appliance has long been known. Current opinion is that the problem of corrosion in glassware is the result of two separate phenomena. On the one hand, the corrosion is clearly due to minerals from the glass composition accompanied by hydrolysis of the silicate network. On the other hand, silicate material is released from the glass. After several washes in an automatic dishwashing appliance, both phenomena can cause damage to glassware such as cloudiness, scratches, and streaks.
Dissolution of the glassware's silicate network is known to be very low at pH values below 9.5 and increases with increasing pH. In institutional and domestic automatic dishwashing compositions, a strongly alkaline solution is produced and is used to wash dishes, glasses, and other cooking and eating utensils. Ordinary tap water can be used in preparing these strongly alkaline cleaning solutions and for rinsing the wash articles subsequent to the cleaning step. However, in European and in some North American (i.e. water softener users) applications, this tap water is often treated (softened) to remove hardness ions such as calcium and magnesium with the result that hard water residues on washware are reduced.
An unfortunate weakness in the performance of institutional and domestic automatic dishwashing compositions, both in compositions which are phosphated (i.e., containing inorganic phosphate builder salts) and those which are nonphosphated, is that they are particularly prone to attacking glasses and plates. Furthermore, the high alkalinity and high levels of builders add to corrosive effect on glassware. Thus, there is a continuing need to develop alternative automatic dishwashing compositions that provide the abovementioned benefits yet reduce the problem of glassware corrosion.
One approach to reducing glassware corrosion is to provide an automatic dishwashing composition comprising silicate. One approach is to provide an automatic dishwashing composition with a mixture of disilicate and metasilicate. Another approach is to provide an additive to an automatic dishwashing composition, such as, a copolymer of an organomineral siliconate, obtained by condensation polymerization of an alkali metal disilicate and an alkali metal siliconate. Another approach is to provide an automatic dishwashing composition with an alkali metal silicate partially substituted with calcium, magnesium, strontium or cerium as counterion. However, automatic dishwashing compositions comprising specific silicates or modified silicates to avoid dishwashing corrosion restricts the type of formulation to which these solutions are applicable. In particular, corrosion of glassware can be quite severe with compositions of low alkalinity, where silicates are of limited use because of their low stability.
Recently, another approach is the use of metal salts, particularly of aluminum, wherein the metal salt is sequestered to form a metal salt-sequestrant complex, such as, an aluminum(III)-sequestrant complex. In one example, a slow-dissolving aluminum salt is sequestered to form the aluminum(III)-sequestrant complex, which is added as a premix to an automatic detergent composition in the absence of silicate. Since these particular salts dissolve at a particular rate, they severely limit the selection of aluminum(III) species, which are useful. Another example of such an approach requires the selection of specific pKas and pHs to form an aluminum/sequestrant premix. However, the usefulness of these aluminum/sequestrant premix formulations is limited. In another example, the aluminum/sequestrant premix must be added as an additional step to the process of forming the detergent compositions which adds cost to its commercial application. In another approach, a fast-dissolving aluminum salt is used yet must be combined with greater than about 10 wt. % silicate in high alkalinity products to avoid corrosion since corrosion is especially pronounced in alkaline automatic dishwashing compositions having an absence of silicate. However, the sequestering process is complicated since is composed of multiple process steps and involves precise adjustment of pH and the aluminum/sequestrant complex is limited to detergent compositions wherein a 1% aqueous solution of the composition has a pH of 9.
A cost effective and simple approach to reducing glassware corrosion is to provide a glasscare active salt, for example an aluminum salt such as aluminum sulfate, to the automatic dishwashing composition. However, there are several drawbacks to this approach. For example, soluble (or slightly soluble) glasscare active salts in gel detergent lead to clumping of the gel product, which can also cause phase separation in certain detergents. These salts can also lead to a reduction in the cleaning performance for tea, stains by interfering with the bleach during the wash cycle.
One way to overcome the drawbacks disclosed above is through encapsulation. A variety of materials and methods can be used to coat particles. The majority of the encapsulation effort, however, has been directed to bleach and enzyme encapsulation. In particular, bleach and enzyme particles can be single-coated with fatty acids, polyvinyl alcohol or polyethylene glycols or double-coated with an inner coat of paraffin or microcrystalline waxes having melting points of 40°–94° C. and a second coat of material such as sodium carbonate. Alternatively, the double-coated encapsulated bleach and enzyme particles may have an inner coat of fatty acid or waxes and an outer coat of water-soluble cellulose ether. Other encapsulating coatings for bleach and enzyme particles include polymer latex; polycarboxylate materials; polyethylene waxes of melting point 50°–65° C.; and various other waxes. The bleach and enzyme particles may also be coated with ethylene vinyl acetate, fatty acid, natural waxes, a synthetic resin or an inorganic coating. For example, the bleach and enzyme particles may be coated with silicone oil, petroleum jelly or alcohol waxes. Some precursor particles used in cleaning compositions have also been encapsulated with liquid paraffin waxes and polyvinyl alcohol.
It has surprisingly been found that by protecting certain glasscare active salts from dissolving in (or reacting with) the detergent composition good glassware corrosion protection can be achieved during washing and/or rinsing cycles of an automatic dishwashing appliance. The drawback of clumping in gels can be avoided and the interaction of the glasscare active salts with detergent components can be minimized in liquids, powders and tablets by use of encapsulated glasscare active salts. The release of the encapsulated glasscare active salt can be delayed or sequenced depending on the type of encapsulating coating used. Thus, by sequencing and/or delaying the release of the glasscare active salts in detergent compositions by encapsulation, bleaching agents, like oxygen bleach, can be used to remove tea stains before the glasscare active salt has time to react with the stain.